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Date:	Wed, 18 May 2016 18:44:55 +0530
From:	Sreekanth Reddy <sreekanth.reddy@...adcom.com>
To:	Calvin Owens <calvinowens@...com>
Cc:	Sathya Prakash Veerichetty <sathya.prakash@...adcom.com>,
	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	Chaitra Basappa <chaitra.basappa@...adcom.com>,
	Suganath Prabu Subramani 
	<suganath-prabu.subramani@...adcom.com>,
	"James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	PDL-MPT-FUSIONLINUX <mpt-fusionlinux.pdl@...adcom.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kernel-team <kernel-team@...com>
Subject: Re: [PATCH] mpt3sas: Do scsi_remove_host() before deleting SAS PHY objects

On Tue, May 17, 2016 at 8:43 AM, Calvin Owens <calvinowens@...com> wrote:
> On Monday 05/16 at 15:51 -0600, Sathya Prakash Veerichetty wrote:
>> Our understanding is the relationship between the SCSI host and SAS end
>> devices is a parent-child and before ripping of SCSI host we need to rip of
>> all the children.
>
> I know at least HPSA does the opposite, Elliott observes that other
> drivers do as well.
>
>> Why the enclosure ends up trying to re-parent the SCSI device from the
>> enclosure to the SAS PHY even after we remove the SAS Phy?
>
> Take this path in /sys:
>
> /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/host6/port-6:0/expander-6:0/port-6:0:0/end_device-6:0:0/target6:0:0/6:0:0:0/scsi_device/6:0:0:0
>
> The problem is "port-6:0:0" in the hierarchy: since mpt3sas explicitly
> calls sas_port_delete() before scsi_remove_host(), that node is removed
> from the device hierarchy and seems to orphan what lies beneath it:
>
> [  955.119328] kobject: '6:0:0:0' (ffff88074e2e1008): kobject_uevent_env
> [  955.133890] kobject: '6:0:0:0' (ffff88074e2e1008): fill_kobj_path: path = '/end_device-6:0:0/target6:0:0/6:0:0:0/bsg/6:0:0:0'
> <WARN/OOPS sadness follows>

[Sreekanth] Calvin, Now with your patch we are observing same type of
<WARN/OOPS> while unregistered the drive with scsi_transport layer
after calling scsi_remove_host() on the same driver unload path,

kobject: 'end_device-2:0' (ffff8800dad0c010): kobject_uevent_env
kobject: 'end_device-2:0' (ffff8800dad0c010): fill_kobj_path: path =
'/host2/port-2:0/end_device-2:0/bsg/end_device-2:0'

As scsi_remove_host() has freed it's parent
"/devices/pci0000:00/0000:00:07.0" we are observing these warnings.

here is it's complete path

 fill_kobj_path: path =
'/devices/pci0000:00/0000:00:07.0/host2/port-2:0/end_device-2:0/bsg/end_device-2:0',

Until on  ~3.19/4.0 kernel all the thing are working fine, we haven't
seen these types of kernel warning. Also we haven't done any changes
in mpt3sas driver w.r.t to this after 4.0 kernel.

>
> As the above from CONFIG_DEBUG_KOBJECT suggests, "end_device-6:0:0" no longer
> has a parent. The path to the enclosured device is:
>
> /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/host6/port-6:0/expander-6:0/port-6:0:15/end_device-6:0:15/target6:0:15/6:0:15:0/enclosure/6:0:15:0/ArrayDevice09
>
> Enclosure wants to re-add the device outside the enclosure:
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/misc/enclosure.c#n404
>
> We melt when trying to re-add "ArrayDevice09" to the "6:0:15:0" directory
> above the "enclosure" directory best I can tell. This is *incredibly*
> confusing because kobj_add_internal() actually clobbers the parent pointer
> if it's NULL:
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/lib/kobject.c#n216
>
> So even though it appears that the parent was "6:0:15:0" here, it was
> actually NULL when passed into kobj_add_internal(). Thus, we try to do
> the add with the kset as our parent, and we get -ENOENT because that
> node has been marked as inactive in kernfs as per here:
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/kernfs/dir.c#n743
>
> Why is it inactive? I think, because __kernfs_remove() deleted an ancestor:
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/kernfs/dir.c#n1243
>
> ...which brings us full circle.
>
>> Doesn't this need to be taken care in enclosure_removal?
>
> Even with enclosure compiled out, I still get a WARN like the following
> for every block device being removed at rmmod (-dirty here is just from me
> applying a fix to SES I sent to the list a few days ago):
>
> [  224.057286] ------------[ cut here ]------------
> [  224.067696] WARNING: CPU: 1 PID: 5412 at fs/sysfs/group.c:237 sysfs_remove_group+0x10f/0x150
> [  224.088007] sysfs group ffffffff83109ba0 not found for kobject 'sdc'
> [  224.102283] Modules linked in: mpt3sas(-) <snip>
> [  224.200483] CPU: 0 PID: 5412 Comm: rmmod Not tainted 4.6.0-dirty #4
> [  224.219797] Hardware name: Wiwynn   HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016
> [  224.237001]  ffffffff82af6280 ffff8806e826f8b0 ffffffff81e13e54 ffff8806e826f928
> [  224.253811]  0000000000000000 ffff8806e826f8f8 ffffffff81127822 ffffffff831a5968
> [  224.270647]  ffff8806000000ed ffffed00dd04df21 0000000000000000 ffff880754ae3078
> [  224.287462] Call Trace:
> [  224.292953]  [<ffffffff81e13e54>] dump_stack+0x68/0x94
> [  224.304433]  [<ffffffff81127822>] __warn+0x172/0x1b0
> [  224.315514]  [<ffffffff811278f7>] warn_slowpath_fmt+0x97/0xb0
> [  224.351845]  [<ffffffff816bbc1f>] sysfs_remove_group+0x10f/0x150
> [  224.365252]  [<ffffffff81377814>] blk_trace_remove_sysfs+0x14/0x20
> [  224.379021]  [<ffffffff81d966bf>] blk_unregister_queue+0xcf/0x120
> [  224.392589]  [<ffffffff81dc8c7e>] del_gendisk+0x26e/0x600
> [  224.432345]  [<ffffffff8215ea75>] sd_remove+0xf5/0x1b0
> [  224.443808]  [<ffffffff820dd210>] __device_release_driver+0x160/0x3a0
> [  224.458151]  [<ffffffff820dd475>] device_release_driver+0x25/0x40
> [  224.471734]  [<ffffffff820dbd81>] bus_remove_device+0x2e1/0x4b0
> [  224.484926]  [<ffffffff820d25ad>] device_del+0x37d/0x680
> [  224.555423]  [<ffffffff82148225>] __scsi_remove_device+0x1e5/0x250
> [  224.569196]  [<ffffffff821443bc>] scsi_forget_host+0x12c/0x1e0
> [  224.582197]  [<ffffffff82120b6c>] scsi_remove_host+0x10c/0x300
> [  224.595227]  [<ffffffffa0066cc9>] scsih_remove+0x339/0x670 [mpt3sas]
> [  224.609383]  [<ffffffff81edd400>] pci_device_remove+0x70/0x110
> [  224.622379]  [<ffffffff820dd210>] __device_release_driver+0x160/0x3a0
> [  224.636724]  [<ffffffff820de7b3>] driver_detach+0x183/0x200
> [  224.649166]  [<ffffffff820dc61f>] bus_remove_driver+0xdf/0x200
> [  224.662185]  [<ffffffff820df2e7>] driver_unregister+0x67/0xa0
> [  224.675009]  [<ffffffff81edb2ee>] pci_unregister_driver+0x1e/0xe0
> [  224.688613]  [<ffffffffa0093a3a>] _mpt3sas_exit+0x23/0x5e9 [mpt3sas]
> [  224.702782]  [<ffffffff812a2d1b>] SyS_delete_module+0x2eb/0x390
> [  224.743359]  [<ffffffff829529e5>] entry_SYSCALL_64_fastpath+0x18/0xa8
> [  224.759036] ---[ end trace 13f1919bf2ec7bb0 ]---
>
> My patch fixes that too :)
>
> The only driver besides mpt*sas that calls sas_delete_port() explicitly is
> HPSA, and it does it in the opposite order mpt3sas does: scsi_remove_host()
> first.
>
> Thanks,
> Calvin
>
>> -----Original Message-----
>> From: Calvin Owens [mailto:calvinowens@...com]
>> Sent: Monday, May 16, 2016 2:25 PM
>> To: Elliott, Robert (Persistent Memory)
>> Cc: Sathya Prakash; Chaitra P B; Suganath Prabu Subramani; James E.J.
>> Bottomley; Martin K. Petersen; MPT-FusionLinux.pdl@...adcom.com;
>> linux-scsi@...r.kernel.org; linux-kernel@...r.kernel.org;
>> kernel-team@...com; calvinowens@...com
>> Subject: Re: [PATCH] mpt3sas: Do scsi_remove_host() before deleting SAS PHY
>> objects
>>
>> On Friday 05/13 at 21:17 +0000, Elliott, Robert (Persistent Memory) wrote:
>> >
>> >
>> > > -----Original Message-----
>> > > From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
>> > > owner@...r.kernel.org] On Behalf Of Calvin Owens
>> > > Sent: Friday, May 13, 2016 3:28 PM
>> > ...
>> > > Subject: [PATCH] mpt3sas: Do scsi_remove_host() before deleting SAS
>> > > PHY objects
>> > >
>> > ...
>> > > The issue is that enclosure_remove_device() expects to be able to
>> > > re-add the device that was previously enclosured: so with SES
>> > > running, the order we unwind things matters in a way it otherwise
>> > > wouldn't.
>> > >
>> > > Since mpt3sas deletes the SAS objects before the SCSI hosts,
>> > > enclosure ends up trying to re-parent the SCSI device from the
>> > > enclosure to the SAS PHY which has already been deleted. This obviously
>> > > ends in sadness.
>> > >
>> > > The fix appears to be simple: just call scsi_remove_host() before we
>> > > call
>> > > sas_port_delete() and/or sas_remove_host().
>> > >
>> > ...
>> > > diff --git a/drivers/scsi/mpt3sas/mpt3sas_scsih.c
>> > > @@ -8149,6 +8149,8 @@ void scsih_remove(struct pci_dev *pdev)
>> > >           _scsih_raid_device_remove(ioc, raid_device);
>> > >   }
>> > >
>> > > + scsi_remove_host(shost);
>> > > +
>> > >   /* free ports attached to the sas_host */
>> > >   list_for_each_entry_safe(mpt3sas_port, next_port,
>> > >      &ioc->sas_hba.sas_port_list, port_list) { @@ -8172,7 +8174,6 @@
>> > > void scsih_remove(struct pci_dev *pdev)
>> > >   }
>> > >
>> > >   sas_remove_host(shost);
>> > > - scsi_remove_host(shost);
>> > >   mpt3sas_base_detach(ioc);
>> > >   spin_lock(&gioc_lock);
>> > >   list_del(&ioc->list);
>> >
>> > That change matches the pattern of all other drivers calling
>> > sas_remove_host, except for one:
>> >     drivers/message/fusion/mptsas.c
>> >
>> > That consensus means this comment in drivers/scsi/scsi_transport_sas.c
>> > is wrong:
>> >
>> > /**
>> >  * sas_remove_host  -  tear down a Scsi_Host's SAS data structures
>> >  * @shost:      Scsi Host that is torn down
>> >  *
>> >  * Removes all SAS PHYs and remote PHYs for a given Scsi_Host.
>> >  * Must be called just before scsi_remove_host for SAS HBAs.
>> >  */
>>
>> Yes, exactly: that comment appears to be backwards, and as you say most
>> drivers appear to do the opposite (I looked at HPSA at least, which calls
>> sas_port_delete() before scsi_remove_host()).
>>
>> I suppose I should send a patch to fix the comment as well? It'd be nice to
>> get some testing to be certain I'm not breaking somebody else's setup by
>> fixing mine though...
>>
>> Thanks,
>> Calvin

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